U.S. patent application number 16/834385 was filed with the patent office on 2020-07-16 for resonant illumination driver in an optical distance measurment system.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Subhash Chandra Venkata Sadhu.
Application Number | 20200225323 16/834385 |
Document ID | / |
Family ID | 61009251 |
Filed Date | 2020-07-16 |
United States Patent
Application |
20200225323 |
Kind Code |
A1 |
Sadhu; Subhash Chandra
Venkata |
July 16, 2020 |
Resonant Illumination Driver in an Optical Distance Measurment
System
Abstract
An optical transmitting system for distance measuring includes a
modulation signal generator, a light source, and an illumination
driver coupled to the modulation signal generator and the light
source. The modulation signal generator is configured to generate a
modulation signal. The light source is configured to generate an
optical waveform with amplitude modulation corresponding with the
modulation signal. The illumination driver is configured to drive
the light source. The illumination driver includes a switch and a
switch driver. The switch is configured to switch between an on
state and an off state to drive the light source. The switch driver
is configured to drive the switch between the on and off states.
The switch driver includes a first inductor and a capacitor in
series with the first inductor and the switch.
Inventors: |
Sadhu; Subhash Chandra Venkata;
(Bengaluru, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
61009251 |
Appl. No.: |
16/834385 |
Filed: |
March 30, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15662352 |
Jul 28, 2017 |
10641869 |
|
|
16834385 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 7/4865 20130101;
G01S 17/89 20130101; G01S 17/931 20200101; G01S 7/484 20130101;
G01S 17/10 20130101 |
International
Class: |
G01S 7/484 20060101
G01S007/484; G01S 7/4865 20060101 G01S007/4865; G01S 17/10 20060101
G01S017/10; G01S 17/89 20060101 G01S017/89 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 2016 |
IN |
201641026036 |
Claims
1. An optical transmitting system for distance measuring,
comprising: a modulation signal generator configured to generate a
modulation signal; a light source configured to generate an optical
waveform with amplitude modulation corresponding with the
modulation signal; and an illumination driver coupled to the
modulation signal generator and the light source, the illumination
driver configured to drive the light source, the illumination
driver including: a switch configured to switch between an on state
and an off state to drive the light source; and a switch driver
configured to drive the switch between the on and off states, the
switch driver including a first inductor and a capacitor in series
with the first inductor and the switch.
2. The optical transmitting system of claim 1, wherein a
capacitance of the capacitor is less than a gate capacitance of the
switch.
3. The optical transmitting system of claim 2, wherein the
capacitance of the capacitor is at least ten times less than the
gate capacitance of the switch.
4. The optical transmitting system of claim 1, wherein: a first end
of the first inductor is connected to a first end of a second
inductor and a second end of the first inductor is connected to the
capacitor; a second end of the second inductor is connected to a
source of the switch; and the capacitor is connected to a gate of
the switch.
5. The optical transmitting system of claim 4, wherein an
inductance of the second inductor is less than an inductance of the
first inductor.
6. The optical transmitting system of claim 1, wherein the switch
is an n-type metal oxide semiconductor (NMOS) transistor.
7. A resonant illumination driver, comprising: a first inductor
configured to receive a drive current; a second inductor in a
series with the first inductor; a capacitor in series with the
first and second inductors; and a power transistor in series with
the capacitor, the power transistor configured to switch between an
on state and an off state to drive a light source.
8. The resonant illumination driver of claim 7, wherein the first
and second inductors are configured to generate a voltage at the
capacitor sufficient to drive a gate of the power transistor to
switch from the off state to the on state.
9. The resonant illumination driver of claim 8, wherein: a first
end of the first inductor is connected to a first end of the second
inductor and a second end of the first inductor is connected to the
capacitor; a second end of the second inductor is connected to a
source of the power transistor; and the capacitor is connected to
the gate of the power transistor.
10. The resonant illumination driver of claim 9, wherein an
inductance of the first inductor is greater than an inductance of
the second inductor.
11. The resonant illumination driver of claim 7 wherein a gate
capacitance of the power transistor is greater than a capacitance
of the capacitor.
12. A three dimensional (3D) time of flight (TOF) camera,
comprising: a transmitter configured to generate an optical
waveform with amplitude modulation corresponding with a frequency
of a generated modulation signal, the transmitter including an
illumination driver configured to drive a light source that
generates the optical waveform, the illumination driver including:
a switch configured to switch between an on state and an off state
to drive the light source; and a switch driver configured to drive
the switch between the on and off states, the switch driver
including a first inductor and a second inductor in a split
configuration with the first inductor and a capacitor in series
with the first and second inductors and the switch; and a receiver
configured to receive the optical waveform reflected off of a
target object and determine a distance to the target object based
on a TOF from the transmitter to the target object and back to the
receiver.
13. The 3D TOF camera of claim 12, wherein a capacitance of the
capacitor is less than a gate capacitance of the switch.
14. The 3D TOF camera of claim 12, wherein: a first end of the
first inductor is connected to a first end of the second inductor
and a second end of the first inductor is connected to the
capacitor; a second end of the second inductor is connected to a
source of the switch; the capacitor is connected to a gate of the
switch; and an inductance of the first inductor is greater than an
inductance of the second inductor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This continuation application claims priority to U.S. patent
application Ser. No. 15/662,352, filed Jul. 28, 2017, which claims
priority to Indian Provisional Patent Application No. 201641026036,
filed Jul. 29, 2016, both of which are hereby incorporated herein
by reference in their entirety.
BACKGROUND
[0002] Optical time of flight (TOF) systems generally use optical
light signals to measure distances to objects based on the time of
flight of the light signal to the target object and back to the
system. For example, three-dimensional (3D) TOF camera systems work
by measuring the distance to a target object by reflecting light
off of one or more targets and analyzing the reflected light. More
specifically, 3D TOF camera systems typically determine a time of
flight (TOF) for the light pulse to travel from the light source
(e.g., a laser or light emitting diode (LED)) to a target object
and return by analyzing the phase shift between the reflected light
signal and the transmitted light signal. The distance to the target
object then may be determined. An entire scene is captured with
each transmitted light pulse. These systems may be used in many
applications including: geography, geology, geomorphology,
seismology, transport, human-machine interfaces, machine vision,
and remote sensing. For example, in transportation, automobiles may
include 3D TOF camera systems to monitor the distance between the
vehicle and other objects (e.g., another vehicle). The vehicle may
utilize the distance determined by the 3D TOF camera system to, for
example, determine whether the other object, such as another
vehicle, is too close, and automatically apply braking.
SUMMARY
[0003] In accordance with at least one embodiment of the
disclosure, an optical transmitting system for distance measuring
includes a modulation signal generator, a light source, and an
illumination driver coupled to the modulation signal generator and
the light source. The modulation signal generator is configured to
generate a modulation signal. The light source is configured to
generate an optical waveform with amplitude modulation
corresponding with the modulation signal. The illumination driver
is configured to drive the light source. The illumination driver
includes a switch and a switch driver. The switch is configured to
switch between an on state and an off state to drive the light
source. The switch driver is configured to drive the switch between
the on and off states. The switch driver includes a first inductor
and a capacitor in series with the first inductor and the
switch.
[0004] Another illustrative embodiment is a resonant illumination
driver that includes a first inductor, a second inductor in series
with the first inductor, a capacitor in series with the first and
second inductors, and a power transistor in series with the
capacitor. The first inductor is configured to receive a drive
current. The power transistor is configured to switch between an on
state and an off state to drive a light source.
[0005] Yet another illustrative embodiment is a 3D TOF camera that
includes a transmitter and a receiver. The transmitter is
configured to generate an optical waveform with amplitude
modulation corresponding with a frequency of a generated modulation
signal. The transmitter includes an illumination driver configured
to drive a light source that generates the optical waveform. The
illumination driver includes a switch and a switch driver. The
switch is configured to switch between an on state and an off state
to drive the light source. The switch driver is configured to drive
the switch between the on and off states. The switch driver
includes a first inductor and a second inductor in a split
configuration with the first inductor and a capacitor in series
with the first and second inductors and the switch. The receiver is
configured to receive the optical waveform reflected off of a
target object and determine a distance to the target object based
on a TOF from the transmitter to the target object and back to the
receiver.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a detailed description of various examples, reference
will now be made to the accompanying drawings in which:
[0007] FIG. 1 shows an illustrative optical time of flight system
in accordance with various examples;
[0008] FIG. 2 shows an illustrative transmitter for an optical time
of flight system in accordance with various examples;
[0009] FIG. 3 shows an illustrative illumination driver for a
transmitter for an optical time of flight system in accordance with
various examples;
[0010] FIG. 4 shows multiple illustrative voltage versus time
graphs at various nodes in an illumination driver for a transmitter
for an optical time of flight system in accordance with various
examples;
[0011] FIG. 5A shows an illustrative receiver for an optical time
of flight system in accordance with various examples; and
[0012] FIG. 5B shows an illustrative receiver for an optical time
of flight system in accordance with various examples.
NOTATION AND NOMENCLATURE
[0013] Certain terms are used throughout the following description
and claims to refer to particular system components. As one skilled
in the art will appreciate, companies may refer to a component by
different names. This document does not intend to distinguish
between components that differ in name but not function. In the
following discussion and in the claims, the terms "including" and
"comprising" are used in an open-ended fashion, and thus should be
interpreted to mean "including, but not limited to . . . ." Also,
the term "couple" or "couples" is intended to mean either an
indirect or direct connection. Thus, if a first device couples to a
second device, that connection may be through a direct connection,
or through an indirect connection via other devices and
connections. The recitation "based on" is intended to mean "based
at least in part on." Therefore, if X is based on Y, X may be based
on Y and any number of other factors.
DETAILED DESCRIPTION
[0014] The following discussion is directed to various embodiments
of the disclosure. Although one or more of these embodiments may be
preferred, the embodiments disclosed should not be interpreted, or
otherwise used, as limiting the scope of the disclosure, including
the claims. In addition, one skilled in the art will understand
that the following description has broad application, and the
discussion of any embodiment is meant only to be exemplary of that
embodiment, and not intended to intimate that the scope of the
disclosure, including the claims, is limited to that
embodiment.
[0015] Optical TOF systems, such as 3D TOF cameras, point Light
Detection and Ranging (LiDAR, LIDAR, lidar, LADAR), and scanning
LIDAR, determine distances to various target objects utilizing the
TOF of an optical signal (e.g., a light signal) to the target
object and its reflection off a target object back to the TOF
system (return signal). These systems can be used in many
applications including: geography, geology, geomorphology,
seismology, transport, and remote sensing. For example, in
transportation, automobiles can include 3D cameras to monitor the
distance between the vehicle and other objects (e.g., another
vehicle). The vehicle can utilize the distance determined by the 3D
camera to, for example, determine whether the other object, such as
another vehicle, is too close, and automatically apply braking.
[0016] The optical signals are generated by a light source (e.g., a
laser diode, light emitting diode, etc.) driven by an illumination
driver. In order to generate amplitude modulated optical signals,
which are utilized in many optical TOF systems, the illumination
driver hard switches one or more power switches (e.g., a power
metal-oxide-semiconductor field effect transistor (MOSFET)) at a
modulation signal frequency. The frequency of switching is
typically in the tens to hundreds of MHz. At these frequencies, the
gate capacitances of the power switches, which typically have a
drain-to-source resistance when closed of a few milliohms, are
relatively high and demand a relatively high amount of power (e.g.,
approximately 1 W). Conventional illumination drivers either
directly drive the gate of the power switch or use a simple
resonant circuit that uses the gate capacitance of the power switch
and a single inductor. However, due to the high frequency of
switching, directly driven drivers have high gate driving losses in
the tens of MHz. Additionally, it is difficult to drive low
drain-to-source resistance when closed switches at a tens to
hundreds of MHz switching frequency. For simple resonant circuits,
the gate capacitance is variable at each switch. Thus, it is
difficult to utilize a single design across different devices.
Furthermore, the gate capacitance changes as temperature changes.
Thus, the switching frequency generated by the illumination driver
can deviate from the desired frequency. Thus, there is a need for
an illumination driver that reliably provides switching to a power
switch at a frequency in the tens to hundreds of MHz to drive a
light source in an optical TOF system.
[0017] In accordance with various examples, an optical TOF system
is provided with an illumination driver that includes a resonant
circuit with a resonant frequency that is unaffected by the gate
capacitance of the power switch. The resonant circuit includes, in
an embodiment, two inductors in a split configuration in series
with a relatively low capacitance capacitor and the gate of the
power switch. The resonant frequency of the circuit is determined
based on the value of the inductance of the two inductors and the
capacitance of the capacitor. By adding the series capacitor, the
resonant frequency of the resonant circuit is unaffected by the
gate capacitance of the power switch because the effective
capacitance of the resonant circuit is equal to the capacitance of
the series capacitor which does not vary across devices and is
temperature invariant. Hence, the resonant frequency of the
illumination driver can be reliably generated without the need to
compensate for temperature and/or device variations.
[0018] To provide the necessary voltage to drive the gate of the
power switch with a relatively low capacitance series capacitor
while ensuring compatibility with complementary metal-oxide
semiconductor (CMOS) design limitations, the combination of the
split inductors can generate higher voltages (e.g., up to 50V) at
the input of the series capacitor. Therefore, the illumination
driver can generate a voltage that can open and close the power
switch even in the presence of the relatively low capacitance
series capacitor.
[0019] FIG. 1 shows an illustrative optical TOF system 100 in
accordance with various examples. In some embodiments, the optical
TOF system 100 is a 3D TOF camera. However, the optical TOF system
100 can be any type of optical TOF system (e.g., point LIDAR,
scanning LIDAR, etc.). The optical TOF system 100 includes a
transmitter 102, receiver 110, and controller 112. The transmitter
102 is configured, by the controller 112, to generate one or more
optical waveforms 152. The controller 112 can be implemented as a
processor (e.g., a microcontroller, a general-purpose processor,
etc.) that executes instructions retrieved from a storage device,
or as dedicated hardware circuitry. In some embodiments, the
optical waveform 152 is a single tone (e.g., a continuous wave)
with amplitude modulation (e.g., a continuous amplitude modulated
waveform).
[0020] The transmitter 102 is also configured, in an embodiment, to
direct the optical waveform 152 toward the field of view (FOV) 106.
In some embodiments, the transmitter 102 directs the optical
waveform 152 toward the FOV 106 by directing the optical waveform
152 directly to the FOV 106. In other embodiments, the transmitter
102 directs the optical waveform 152 toward the FOV 106 by
directing the optical waveform to a beam steering device (not
shown) which then directs the optical waveform 152 to the FOV 106.
In such embodiments, the beam steering device receives the optical
waveform 152 from the transmitter 102 and steers the optical
waveform 152 to the FOV 106. Thus, the transmitter 102 can direct
the optical waveform 152 directly to the target object 106 or can
direct the optical waveforms 152 to a beam steering device which
directs the optical waveform 152 to the FOV 106.
[0021] The optical waveform 152 (or optical waveforms 152) reflects
off of any objects located within the FOV 106 (i.e., target
objects) and returns toward the receiver 110 as reflected optical
waveform 162. The reflected optical waveform 162 is then received
by the receiver 110. In some embodiments, an additional beam
steering device (not shown) steers the reflected optical waveform
162 to the receiver 110. In some embodiments, the receiver 110
receives the reflected optical waveform 162 directly from the
target object 106.
[0022] The receiver 110 is configured to receive the reflected
optical waveform 162 and determine the distance to the target
objects within FOV 106 based on the TOF from the transmitter 102 to
the target object 106 and back to the receiver 110. For example,
the speed of light is known, so the distance to the target objects
is determined and/or estimated using the TOF. That is, the distance
is estimated as d=c*TOF/2 where d is the distance to the target
object, c is the speed of light, and TOF is the time of flight. The
speed of light times the TOF is halved to account for the travel of
the light pulse to, and from, the target object.
[0023] In some embodiments, the receiver 110, in addition to
receiving the reflected optical waveform 162 reflected off of the
target object 106, is also configured to receive the optical
waveform 152, or a portion of the optical waveform 152, directly
from the transmitter 102. The receiver 110, in an embodiment, is
configured to convert the two optical signals into electrical
signals, a received signal corresponding to the reflected optical
waveform 162 and a reference signal corresponding to the optical
waveform 152 received directly from the transmitter 102. The
receiver 110 then, in an embodiment, performs a correlation
function using the reference signal and the received signal. A peak
in the correlation function corresponds to the time delay of the
received reflected optical waveform 162 (i.e., the TOF). The
distance then can be estimated using the formula discussed above.
In other embodiments, a fast Fourier transform (FFT) can be
performed on the received signal. A phase of the tone then is used
to estimate the delay (i.e., TOF) in the received signal. The
distance then can be estimated using the formula discussed above.
In yet other embodiments, the in-phase (I) component is determined
by correlating the received reflected optical waveform 162 with the
transmitted optical waveform 152 received directly from the
transmitter 102, and the quadrature (Q) component is determined by
correlating the received reflected optical waveform 162 with a 90
degree phase shifted version of the transmitted optical waveform
152 received directly from the transmitter 102. The I/Q integrated
charges are used to estimate the phase shift between the optical
waveform 152 received directly from the transmitter 102 and the
received reflected optical waveform 162. The distance then can be
estimated using the formula discussed above.
[0024] FIG. 2 shows an illustrative transmitter 102 for optical TOF
system 100 in accordance with various examples. The transmitter
102, in an embodiment, includes a modulation signal generator 202,
an illumination driver 206, a light source 208, and an optics
device 210. The modulation signal generator 202 is configured to
generate a modulation signal (e.g., a modulation reference signal)
and continuous waveforms using the modulation signal. For example,
in some embodiments, the modulation signal generator 202 is
configured to generate a single tone (i.e. continuous wave)
modulation signal. The amplitude of the carrier signal, which in an
embodiment is also generated by the modulation signal generator
202, is modulated with the modulation signal to generate a
modulated carrier signal.
[0025] The illumination driver 206 generates a driving signal
(regulates the current) to drive one or more optical transmitters,
such as light source 208, so that the optical transmitter generates
optical transmission signal 152 that corresponds with the modulated
carrier signal generated by the modulation signal generator 202. In
other words, the modulation signal modulates the intensity of the
light transmitted by light source 208 during the pulse with the
illumination driver 206 providing the driving current to the light
source 208. The amplitude of the modulated carrier signal, and
thus, the amplitude of the optical waveform 152 depends on and
thus, corresponds with, the frequency of the modulation signal.
While light source 208 is shown in FIG. 2 as a laser diode, any
type of optical signal generator (e.g., a light emitting diode
(LED)) can be utilized to generate the optical waveform 152. The
optical device 210, which, in an embodiment is one or more lenses,
is configured to direct (e.g., focus) the optical waveform 152
(e.g., the modulated light signal) toward the FOV 106.
[0026] FIG. 3 shows an illustrative illumination driver 206 for
transmitter 102 for optical TOF system 100 in accordance with
various examples. The illumination driver 206, in an embodiment,
includes a switch driver 302 and a switch 304. The switch driver
302 is configured to drive the gate of switch 304 with a voltage
and/or current signal to open and close switch 304. In other words,
the switch driver 302 generates a voltage and/or current that
causes the switch 304 to enter an on state (the switch closes) and
then a voltage and/or current that causes the switch 304 to enter
an off state (the switch opens). More particularly, in an
embodiment, the switch driver 302 generates a voltage that is
greater than the threshold voltage of the switch 304 thereby
closing the switch 304 (causing the switch 304 to enter the on
state) alternating with generating a voltage that is less than the
threshold voltage of the switch 304 thereby opening the switch 304
(causing the switch 304 to enter the off state).
[0027] In some embodiments, the switch 304 is configured to switch
between the on state and the off state at a frequency in the tens
of MHz up to 200 MHz. The switching of the switch 304, along with,
in some embodiments, additional similar switches provides the drive
current to drive the light source 208. More particularly, the
amplitude modulation of optical signal 152 is determined by the
switching frequency of the switch 304 which, in turn, corresponds
with the carrier modulated signal generated by the modulation
signal generator 202. In some embodiments, switch 302 is a power
transistor. More particularly, the switch 304, in some embodiments,
is a power n-type metal oxide semiconductor (NMOS) field-effect
transistor. However, switch 304 can be any type of electrical
switch, such as a p-type metal oxide semiconductor (PMOS)
field-effect transistor, a binary junction transistor (BJT),
etc.
[0028] The switch driver 302 includes, in an embodiment, a level
shifter 306, a resistor 308, inductors 310-312, and capacitor 314.
Level shifter 306 is configured to shift the low and high levels of
a digital signal output from one part of a system to different low
and high levels required by another part of the system. For
example, one part of an electrical system may operate as 1.5V CMOS,
where LOW (i.e., 0) is represented by a voltage between 0 and 0.1V
and HIGH (i.e., 1) is represented by a voltage between 1.4V and
1.5V, while the illumination driver 208 operates as 5V CMOS, where
LOW is represented by a voltage between 0 and 0.1V and HIGH is
represented by a voltage between 4.9V and 5.0V. In other words,
level shifter 306 is configured to shift the HIGH signal from being
represented by a voltage between 1.4V and 1.5V to being represented
by a voltage between 4.9V and 5.0V. Thus, the level shifter 306
acts as a current and/or voltage source for the switch driver
302.
[0029] The inductors 310-312 and capacitor 314 are configured as a
resonant circuit with a resonant frequency that is approximately
(i.e., plus or minus 10%) equal to the frequency of the modulation
signal. Thus, the switch 304 switches between the on state and the
off state at the modulation signal frequency, creating the desired
amplitude modulation in the optical waveform 152. More
particularly, the inductors 310 and 312 are in a split
configuration. The capacitor 314 is in series with the inductors
310-312. For example, the inductor 310 includes a first end which
is connected to a first end of the inductor 312 and a second end
which is connected to the capacitor 314. In addition to being
connected to inductor 310 at its first end, inductor 312 is
connected at a second end to the source of switch 304. In addition
to being connected to the second end of inductor 310, capacitor 314
is connected to the gate of switch 304.
[0030] In some embodiments, the capacitance of the capacitor 314 is
less than the gate capacitance of the switch 304. For example, the
capacitance of the capacitor 314 can be on the order of 50 pF while
the gate capacitance of the switch 304 generally ranges from
hundreds of pF to approximately 1 nF. Thus, the capacitance of the
capacitor 314 is, in an embodiment, at least less than 10 times
less than the gate capacitance of the switch 304. Hence, the
combination of the capacitor 314 with the gate capacitance of the
switch 304 acts as a capacitive divider with most of the voltage
across the capacitor 314. Thus, the effective capacitance of the
resonant circuit (switch driver 302) is equal to the capacitance of
the capacitor 314.
[0031] As discussed above, conventional simple resonant circuit
switch drivers use only the gate capacitance of the power switch to
create the resonant circuit. However, the gate capacitance of the
power switch varies across devices and even within the same switch
as temperatures change. Thus, it is difficult to generate/maintain
the desired resonant frequency, and thus, the desired switching
frequency. By adding the series capacitor 314, the resonant
frequency of the switch driver 302 is unaffected by the gate
capacitance of the switch 304 because the effective capacitance of
the resonant circuit is equal to the capacitance of the capacitor
314 which does not vary across devices and is temperature
invariant. Hence, the resonant frequency of the switch driver 302
can be reliably generated without the need to compensate for
temperature and/or device variations.
[0032] The gate threshold voltage of the switch 304 is, in an
embodiment, approximately 5V. Because the series capacitor 314 is
included in the switch driver 302, a relatively high voltage (e.g.,
20V to 50V) is applied to the capacitor 314 to drive the gate of
switch 304 at approximately 5V. However, output voltages in CMOS
systems are typically limited to a maximum of 5V. Therefore, given
the limitations of the available CMOS drive output voltages, the
combination of inductors 310 and 312 ensures sufficient voltage at
the gate of switch 304 while ensuring compatibility with the
excitation circuit. In an embodiment, the inductance of inductor
312 is less than the inductance of inductor 310. Because the
inductors 310-312 are in series, the combination of inductors
310-312 can generate higher voltages (e.g., up to 50V) at the input
of capacitor 314. Therefore, the switch driver 302 can generate the
5V to switch the switch 304 between the on and off states.
Additionally, in some embodiments, the direct current (DC) voltage
at the gate of switch 304 is maintained by a high impedance voltage
source (not shown) and a capacitor (not shown) is added in series
with the switch driver 302 to avoid DC losses to the switch driver
302.
[0033] The illumination driver 206 has several advantages over
conventional LC resonant drivers. For example, the series
capacitance added by capacitor 314 may ensure that there is
negligible or no frequency dependency on the gate capacitance of
switch 304. Thus, there is negligible or no frequency variations
from board to board. Additionally, without the capacitor 314, the
inductance values for a 50 MHz switching frequency would be
approximately 10 nH-20 nH which is low enough to make the
illumination driver 206 susceptible to board and/or package
parasitic inductance. However, with the inductors 310-312 and
series capacitor 314, the inductance is, in some embodiments, 100
nH-200 nH which is high enough to make the illumination driver not
susceptible to board and/or package parasitic inductance.
Furthermore, a single design can be utilized for many different
drivers instead of each driver having to be designed for the
specific switch in that driver.
[0034] Moreover, the illumination driver 206 has several advantages
over conventional direct switch drivers. For example, there are
lower gate driving losses in the illumination driver 206.
Additionally, it is possible to drive lower drain-to-source
resistance switches which have higher gate capacitance with
illumination driver 206. Furthermore, the power levels required by
illumination driver 206 are much lower (e.g., 150 mW) than the
conventional direct switch drivers (e.g., 1 W).
[0035] FIG. 4 shows multiple illustrative voltage versus time
graphs 402-408 at various nodes 322-328, respectively, in
illumination driver 206 for transmitter 102 for optical TOF system
100 in accordance with various examples. The graph 402 shows an
example voltage versus time graph for the voltage level at the node
322 in FIG. 3 (labelled as V.sub.322). As shown in graph 402, the
voltage is, in an embodiment, level shifted by level shifter 306 to
a 5V peak square waveform.
[0036] As shown in example graph 404, the voltage at node 324 (the
node between the split inductors 310-312 and labelled as
V.sub.324), is a sine waveform created from the square waveform
V.sub.322 shown in graph 402. The waveform V.sub.324 peaks at 1.5V
and oscillates between -1.5V and 1.5V. As shown in example graph
406, the voltage at node 326 (the node between the inductor 310 and
capacitor 314 and labelled as V.sub.326), is a sine waveform
created from the waveform V.sub.324 shown in graph 404. The
waveform V.sub.326 peaks at 20V and oscillates between -20V and
20V. Thus, the inductors 310-312, as discussed above, are able to
generate a relatively large voltage at the capacitor 314. As shown
in example graph 408, the voltage at node 328 (the node between the
capacitor 314 and the gate of the switch 304 and labelled as
V.sub.328), is a sine waveform created from the waveform V.sub.326
shown in graph 406. The waveform V.sub.328 peaks at 5V and
oscillates between 0V and 5V. Thus, the inductors 310-312 and
capacitor 314, as discussed above, are able to generate a gate
drive voltage to open and close switch 304 at the resonant
frequency which, in an embodiment, is approximately equal to the
modulation signal frequency. In this way, the illumination driver
206 drives the light source 208 at a switching frequency which
causes the light source 208 to generate the optical waveform 152
with the desired amplitude modulation.
[0037] FIG. 5A shows an illustrative optical receiver 110 for
optical TOF system 100 in accordance with various examples. The
receiver 110 includes, in an embodiment, an optics device 510
(e.g., a lens), two photodiodes 502 and 512, two trans-impedance
amplifiers (TIAs) 504 and 514, two analog-to-digital converters
(ADCs) 506 and 516, and a receiver processor 508. As discussed
above, in an embodiment, the reflected optical waveform 162 is
received by the receiver 110 after reflecting off of target objects
within the FOV 106. The optics device 510, in an embodiment,
receives the reflected optical waveform 162. The optics device 510
directs (e.g., focuses) the reflected optical waveform 162 to the
photodiode 512. The photodiode 512 is configured to receive the
reflected optical waveform 162 and convert the reflected optical
waveform 162 into a current received signal 552 (a current that is
proportional to the intensity of the received reflected light). TIA
514 is configured to receive the current received signal 552 and
convert the current received signal 552 into a voltage signal,
designated as voltage received signal 554 that corresponds with the
current received signal 552. ADC 516 is configured to receive the
voltage received signal 554 and convert the voltage received signal
554 from an analog signal into a corresponding digital signal,
designated as digital received signal 556. Additionally, in some
embodiments, the current received signal 552 is filtered (e.g.,
band pass filtered) prior to being received by the TIA 514 and/or
the voltage received signal 554 is filtered prior to being received
by the ADC 516. In some embodiments, the voltage received signal
554 is received by a time to digital converter (TDC) (not shown) to
provide a digital representation of the time that the voltage
received signal 554 is received.
[0038] Photodiode 502, in an embodiment, receives the optical
waveform 152, or a portion of the optical waveform 152, directly
from the transmitter 102 and converts the optical waveform 152 into
a current reference signal 562 (a current that is proportional to
the intensity of the received light directly from transmitter 102).
TIA 504 is configured to receive the current reference signal 562
and convert the current reference signal 562 into a voltage signal,
designated as voltage reference signal 564 that corresponds with
the current reference signal 562. ADC 506 is configured to receive
the voltage reference signal 564 and convert the voltage reference
signal 564 from an analog signal into a corresponding digital
signal, designated as digital reference signal 566. Additionally,
in some embodiments, the current reference signal 562 is filtered
(e.g., band pass filtered) prior to being received by the TIA 504
and/or the voltage reference signal 564 is filtered prior to being
received by the ADC 506. In some embodiments, the voltage reference
signal 564 is received by a TDC (not shown) to provide a digital
representation of the time that the voltage reference signal 564 is
received.
[0039] The processor 508 is any type of processor, controller,
microcontroller, and/or microprocessor with an architecture
optimized for processing the digital received signal 556 and/or the
digital reference signal 566. For example, the processor 508 can be
a digital signal processor (DSP), a central processing unit (CPU),
a reduced instruction set computing (RISC) core such as an advanced
RISC machine (ARM) core, a mixed signal processor (MSP), etc. In
some embodiments, the processor 508 is a part of the controller
112. The processor 508, in an embodiment, acts to demodulate the
digital received signal 556 and the digital reference signal 566
based on the modulation signal generated by the modulation signal
generator 202. In some embodiments, the processor 508 also receives
the digital representation of the times that the voltage received
signal 556 and the digital reference signal 566 were received. The
processor 508 then determines, in an embodiment, the distance to
target objects within the FOV 106 by, as discussed above,
performing a correlation function using the reference signal and
the received signal. A peak in the correlation function corresponds
to the time delay of each received reflected optical waveform 162
(i.e., the TOF). The distance to the target object 106 can be
estimated using the formula discussed above. In other embodiments,
an FFT is performed on the received digital signal 556. A phase of
the tone then is used to estimate the delay (i.e., TOF) in the
received signals. The distance then can be estimated using the
formula discussed above.
[0040] FIG. 5B shows another illustrative receiver 102 for optical
TOF system 100 in accordance with various examples. The example
receiver 102 shown in FIG. 5B is an I/Q receiver. The receiver 102
includes a photodiode 582, two switches 586 and 596, and two
capacitors 584 and 594. The photodiode 582 receives the reflected
optical waveform 162 from the target object 106 and converts the
reflected optical waveform 162 into a current which is proportional
to the amount of light being received by the photodiode 582.
Because the amplitude of the reflected optical waveform 162 is
being modulated, this current is representative of the amplitude
modulation of the reflected optical waveform 162 and thus, the
transmitted optical waveform 152. By closing switch 586, this
current is integrated on capacitor 584. The capacitor 584
integrates the current and collects charge. The switch 586, in an
embodiment, is opened and closed using the modulation signal
generated by the modulation signal generator 202. This correlates
the transmitted optical waveform 152 with the received reflected
optical waveform 162. Thus, the charge on the capacitor 584 is
effectively the correlation of the received reflected optical
waveform 162 with the modulation signal. The switch 596 is closed
using an orthogonal (90 degree phase shifted) version of the
modulation signal (the quadrature phase). Thus, the capacitor 594
integrates the current and collects charge based on this quadrature
phase of the modulation signal. This correlates the quadrature
phase of the transmitted optical waveform 152 with the received
reflected optical waveform 162. The charge on capacitors 584 and
594 represent the result of the correlation of the received
reflected optical signal 162 with respect to the transmitted
optical signal 152. This is then used to calculate the distance to
the target object 106 as discussed above.
[0041] In other words, the I/Q receiver 110 shown in FIG. 5B
converts the received reflected optical waveform 162 into an
electrical received signal (e.g., a current). This electrical
received signal is correlated with the modulated carrier signal
generated by the modulation signal generator 202 (corresponding to
the transmitted optical signal 152) to generate an I component. The
electrical received signal is also correlated with a 90 degree
phase shifted version of the modulated carrier signal to generate a
Q component. The phase shift between the electrical received signal
and the modulated carrier signal is estimated based on the I
component and the Q component. This phase shift is converted into
the distance to the target object as discussed above.
[0042] The above discussion is meant to be illustrative of the
principles and various embodiments of the present disclosure.
Numerous variations and modifications will become apparent to those
skilled in the art once the above disclosure is fully appreciated.
It is intended that the following claims be interpreted to embrace
all such variations and modifications.
* * * * *